Satoru Umezawa and Skullsnatcher on the battlefield.
Skullsnatcher does not have summoning sickness and cannot be blocked by an opponent.
You control up to seven lands that can tap to produce at least ({2} magic symbol) ({U} magic symbol) ({B} magic symbol) ({B} magic symbol) .
Steps
Declare Skullsnatcher as an attacker.
When it isn't blocked, activate up to seven lands you control by tapping them, adding at least ({2} magic symbol) ({U} magic symbol) ({B} magic symbol) ({B} magic symbol) .
Activate Great Whale's ninjutsu ability by paying ({2} magic symbol) ({U} magic symbol) ({B} magic symbol) and returning Skullsnatcher from the battlefield to your hand, putting Great Whale onto the battlefield from your hand tapped and attacking.
When Great Whale enters the battlefield, it triggers, untapping up to seven lands.
Activate Skullsnatcher's ninjutsu ability by paying ({B} magic symbol) and returning Great Whale from the battlefield to your hand, putting Skullsnatcher onto the battlefield from your hand tapped and attacking.
Repeat from step 2.
If you control up to seven lands that can tap to produce at least ({3} magic symbol) ({U} magic symbol) ({B} magic symbol) ({B} magic symbol) , this combo nets infinite mana.